This invention relates generally to gas turbine engines and more particularly, to methods and apparatus for assembling gas turbine engine struts.
At least some known gas turbine engines include one or more rotor shafts supported by bearings which, in turn, are supported by annular frames. Each frame includes an annular casing spaced radially outwardly from an annular hub and a plurality of circumferentially spaced apart struts extending therebetween which direct a pre-determined air flow downstream from the frame. The struts may be integrally formed with the casing and hub in a common casting, for example, or may be suitably bolted thereto. Each strut includes a pair of sidewalls coupled at a leading edge and a trailing edge, such that a cavity is defined therebetween.
In either aforementioned strut configuration, the struts facilitate providing structural support to the overall frame, and structural rigidity for supporting the rotor shaft to facilitate minimizing deflections of the shaft during engine operation. Accordingly, the struts are subjected to stresses induced by the engine during operation. Over time, flexture of the strut sidewalls due to low cycle fatigue or high cycle fatigue loading may eventually cause fatigue cracking within the strut sidewalls.
To facilitate reducing the effect of fatigue loading induced to the struts, at least some known struts include a damping device, a room temperature vulcanized (RTV) silicone, or a combination of the two. The damping devices are coupled to the engine frames to facilitate reducing vibrational stresses induced through the struts. However, such devices are expensive and are typically only coupled to the frame when the struts are not coupled in operating position within the gas turbine engine. In addition, a repair to any element of the front frame that requires either brazing or welding, is equally expensive because the whole front frame must be subjected to a heat-treatment process to eliminate localized stresses that could be an initiation sites for subsequent cracks.
The RTV silicones are injected into the strut, cavity to facilitate damping vibrational stresses induced to the strut. However, although such silicones are every cost-affordable in comparison to the damping devices, such silicones may only provide limited vibrational damping, and do not increase the structural integrity of the strut.
In one aspect of the present invention, a method for installing an expandable stiffener is provided. The method comprises providing an assembly including a first sidewall and a second sidewall connected at a leading and trailing edge such that a cavity is defined therebetween, forming an opening extending through the first sidewall and the second sidewall, inserting a first expandable sleeve through the assembly opening such that the sleeve extends between the first and second strut sidewalls, and coupling the sleeve to the first and second sidewalls.
In another aspect of the invention, a strut for a gas turbine engine is provided. The strut includes a first sidewall, a second sidewall, and at least one expandable sleeve. The first sidewall includes an opening extending therethrough. The second sidewall is connected to the first sidewall at a leading edge and at a trailing edge such that a cavity is defined between the first and second sidewalls. The second sidewall includes an opening extending therethrough that is concentrically aligned with respect to the first sidewall opening. The at least one expandable sleeve extends through the first and second sidewall openings and between the first sidewall and the second sidewall. The sleeve is configured to facilitate increasing a fatigue life of s aid strut.